virtualbox.org

I've tried to find a detailed guide on how to share files between the guest and the host OSs, so far I've only found answers in how to move files from the host to the VM but not the other way around. I've a huge file of several Gb that i need to move from my VM into OS X host. How do I do this?

See Chapter 4.3 Shared folders in your VirtualBox users guide.
Once the share is active you just put the file that the host needs in the shared folder. Works both ways.